1. Field of the Invention
The present invention relates generally to a multi-channel contact sensing apparatus, and more particularly, to a multi-channel contact sensing apparatus that simultaneously measures a finger touch input and a pen input.
2. Description of the Related Art
Research is actively being conducted on smart phones as the market associated with smart phones and touch screens has rapidly grown. To input a command associated with a smart phone or a touch screen, a user may designate an icon by designating, on a location of a display, a body portion of the user or an ElectroMagnetic Resonant (EMR) pen.
A touch sensor using a capacitance scheme that is based on the contact of a body portion of the user may respond to only the contact of a conductive object, and has sensitivity that is inversely proportional to the contact area of the conductive object. That is, a change in the capacitance that is a target of the sensor measurement is proportional to the contact area of the conductive object that is in contact with the touch screen. Accordingly, when the contact area is large, a change in a signal increases and thus, the sensor may sufficiently perform sensing. However, when the contact area is small, the probability of malfunction increases. The sensor has a sensitivity that is proportional to the contact area. Thus, a finger that provides a wide contact area with an electrode or a screen is primarily used as an input unit. Accordingly, when using an object other than a finger, such as a pen or a stylus, a contact area may need to be comparable to the contact area of the finger.
An apparatus that uses a pen or a stylus as an input unit may separately use a sensor device, in addition to an existing touch sensor for sensing a finger.
A conventionally used capacitance-type touch sensor is classified into two types based on the role of an electrode used for sensing and the number of electrodes. That is, a type that senses a change in the capacitance between a finger of the user and an electrode contained in a touch screen is referred to as a self capacitive sensing touch screen, and a type that senses variance in capacitance formed between two electrodes in two layers in a touch screen, the variance caused by the contact of the user, is referred to as a mutual capacitive sensing touch screen. The mutual capacitive sensing touch screen may have an advantage in that it may simultaneously recognize multiple contacts correctly. As such, this type of screen has become more freqently utilized.
FIG. 1 illustrates a conventional mutual type touch screen panel. Referring to FIG. 1, the conventional mutual type touch screen panel includes a first electrode layer 11 provided in a lower portion, and a second electrode layer 13 provided on a substrate 15 that is disposed at a distance away from an upper portion of the first electrode layer 11 and has a dielectric constant. The first electrode layer 11 and the second electrode layer 13 are equipped with a plurality of electrode lines that is provided in a cross array. On an upper portion of the touch screen panel, a tempered glass 17 for protecting the second electrode layer 13 is additionally provided.
The first electrode layer 11 is connected to a first circuit to apply a signal, in which case a capacitance is formed between the first electrode layer 11 and the second electrode layer 13 due to the signal, and the signal applied to the first electrode layer 11 through the capacitance is transferred to the second electrode layer 13 and is applied to a second circuit. In the second circuit, it is determined whether a change in the signal transferred from the second electrode layer 13 has occurred, whether a touch is input, and coordinates of a region where the touch is input.
In particular, referring to FIG. 2, when a touch input by a body of a user or a stylus pen 19 does not exist, the signal transferred from the second electrode layer 13 is identical to a reference signal 21. However, when a touch input by a body of the user or the stylus pen 19 exists, a change in a contact strength sensed by the second electrode layer 13 indicates the same pattern as a contact strength signal 22. A change in an amount of an electric field transferred from the second electrode layer 13 of a region where the touch of the body of the user or the touch of the touch stylus pen 19 is input may have a form of an output signal 23. That is, the output signal 23 may have a form that indicates a relatively lower value than a level in a period 24 where the touch input exists, since an amount of electric field coupled from the first electrode layer 11 to the second electrode layer 13 is decreased by the contact of the body of the user or a conductor.
Whether a touch is input is determined by determining the contact strength signal 22 obtained after the process in the second circuit, and coordinates of a region where the touch is input is determined.
A capacitance-type touch sensor, which is widely implemented as a user input device, uses a scheme that senses the variance in capacitance due to a contacted conductor. The scheme readily senses a contact target that has a large contact area and causes a large variance in capacitance, such as a finger, but may have difficulty sensing a pen tip or a stylus, which have a relatively smaller contact area. To improve sensitivity, a threshold level may need to be lowered so that the touch screen responds to a smaller signal change. However, when the threshold level is decreased when a signal to noise ratio greater than or equal to a set level is not secured, the probability of malfunction may increase. According to a method of amplifying a size of a signal, the level of noise may also be amplified unless a method that isolates a noise signal prior to the amplification is secured. Thus, no gain is obtained in terms of the signal to noise ratio, and improved sensitivity is not realized.
As described in the foregoing, the scheme that senses only the variance in capacitance based on a contact area of a conductor has difficulty in sensing an object with a small contact area such as a stylus. Thus, a separate scheme such as a magnetic resonant scheme may be utilized to sense the stylus.
The magnetic resonant scheme may separately require a different electrode device, sensing hardware, and sensing algorithm since the magnetic resonant scheme is different from a scheme for sensing a finger. Accordingly, there is a need in the art for a magnetic resonant scheme employing the proper components and algorithm.